Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2012

Fair Value Measurements

Assets and liabilities measured at fair value on a recurring basis

			Fair value measurements at reporting date using
Description	June 30, 2012		Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
	(Thousands)
Assets
Derivative instruments, at fair value	$	467,587	$	1,688	$	335,352	$	130,547
Total assets	$	467,587	$	1,688	$	335,352	$	130,547
Liabilities
Derivative instruments, at fair value	$	109,214	$	1,534	$	106,569	$	1,111
Total liabilities	$	109,214	$	1,534	$	106,569	$	1,111

			Fair value measurements at reporting date using
Description	December 31, 2011		Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
	(Thousands)
Assets
Derivative instruments, at fair value	$	512,161	$	3,612	$	365,238	$	143,311
Total assets	$	512,161	$	3,612	$	365,238	$	143,311
Liabilities
Derivative instruments, at fair value	$	123,306	$	2,727	$	120,528	$	51
Total liabilities	$	123,306	$	2,727	$	120,528	$	51

Fair value measurements using significant unobservable inputs (Level 3)

	Fair value measurements using significant unobservable inputs (Level 3)
		Derivative instruments, at fair value, net three months ended June 30,						Derivative instruments, at fair value, net six months ended June 30,
		2012			2011			2012			2011
		(Thousands)
Beginning of period		$	156,066		$	97,364		$	143,260		$	116,672
Total gains or losses:
Included in earnings		—			—			—			14
Included in other comprehensive income		(4,203		)	16,851			27,393			11,020
Purchases		(1,016		)	—			(1,016		)	—
Settlements		(21,411		)	(12,243		)	(40,201		)	(25,734		)
Transfers in and/or out of Level 3		—			—			—			—
End of period		$	129,436		$	101,972		$	129,436		$	101,972